Major Diseases of Wheat, Rice and Potato and Their Management

Introduction

Wheat, rice and potato feed more Indians than any other crops, and each has a few diseases that can wipe out a season's profit. Spotting them early and acting the right way makes the difference between a small loss and a failed crop.

Quick answer: The major diseases of wheat are the rusts (yellow, brown and black), Karnal bunt, loose smut and spot blotch. In rice, they are blast, bacterial leaf blight, sheath blight, brown spot, false smut, bakanae and tungro. In potato, they are late blight, early blight, black scurf, common scab, bacterial wilt and aphid-borne viruses. All are best managed with resistant varieties, healthy seed, good field practices and timely, correct use of fungicides.

This guide explains each disease: what causes it, how to recognise it and how to manage it. It extends our earlier posts on diseases of tomato and diseases of rapeseed and mustard.

Table of Contents

1. Crop Disease Calendar at a Glance
2. How to Manage Crop Diseases: The Basics
3. Major Diseases of Wheat
4. Major Diseases of Rice
5. Major Diseases of Potato
6. Using Fungicides Safely
7. Studying Plant Pathology
8. Key Takeaways
9. FAQs

Crop Disease Calendar at a Glance

Each crop has its own disease season, which follows its growing season. Our guide to kharif, rabi and zaid crops explains these seasons in detail.

Crop	Season	Diseases to watch	When the risk is highest
Rice	Kharif (monsoon)	Blast, bacterial leaf blight, sheath blight, brown spot, false smut, bakanae, tungro	Warm, humid monsoon months; bakanae shows from the nursery stage
Wheat	Rabi (winter)	Yellow, brown and black rust, Karnal bunt, loose smut, spot blotch	Cool, damp weather from winter into early spring; smuts show at heading
Potato	Winter crop in the plains	Late blight, early blight, black scurf, common scab, bacterial wilt, viruses	Cool, moist spells in winter for late blight; aphid build-up after early January for viruses

How to Manage Crop Diseases: The Basics

A disease needs three things at the same time: a susceptible crop, the pathogen and favourable weather. Integrated disease management breaks this chain at several points instead of relying on chemicals alone.

• Resistant varieties: the cheapest and most reliable control. Use varieties recommended for your region.
• Healthy seed: many diseases, such as loose smut, bakanae and potato viruses, travel in the seed.
• Field hygiene: remove crop debris, volunteer plants and weed hosts where pathogens survive.
• Balanced nutrition: too much nitrogen makes rice more prone to blast and sheath blight; split the dose.
• Biological control: agents such as Trichoderma and Pseudomonas fluorescens are used against several seed-borne and soil-borne diseases.
• Fungicides: used on time and in the right dose, when monitoring shows they are needed.

Major Diseases of Wheat

Disease	Cause	Key symptoms	Main management
Yellow (stripe) rust	Puccinia striiformis	Yellow powdery stripes on leaves that rub off on fingers	Resistant varieties; destroy volunteer wheat; fungicide spray when patches appear
Brown (leaf) rust	Puccinia triticina	Brown pustules scattered on leaves	Resistant varieties; fungicide spray
Black (stem) rust	Puccinia graminis f. sp. tritici	Reddish-brown pustules on stems that turn black	Resistant varieties; fungicide spray
Karnal bunt	Tilletia indica	Grains partly turned into a black, powdery mass	Disease-free seed; seed treatment; crop rotation
Loose smut	Ustilago tritici	Ears replaced by masses of black spores	Disease-free seed; seed treatment with carboxin
Spot blotch	Bipolaris sorokiniana	Brown spots that merge and cover the leaf	Healthy seed; seed treatment; crop rotation

Wheat rusts

Rusts are the most important diseases of wheat. Yellow rust is a major disease of the North-Western Plains and Northern Hills zones; it spreads easily when cool weather sets in, and infected patches spread in the direction of the wind. The pathogens survive on volunteer wheat and grasses and in the cooler hills, such as the Himalayas in the north and the Nilgiri and Palani hills in the south.

• Grow rust-resistant varieties recommended for your zone; HD 3226 (Pusa Yashasvi), for example, is noted for its resistance to the major rusts.
• Destroy volunteer wheat plants, ideally as a village-wide effort.
• Inspect fields in cool, damp weather. If rust appears in patches, the Indian Institute of Wheat and Barley Research (ICAR-IIWBR) advises spraying a fungicide; propiconazole and tebuconazole are among those used.

Karnal bunt

Karnal bunt, caused by Tilletia indica, damages the grain itself: infected grains are partly converted into black, powdery spores. No resistant varieties are currently available, so prevention matters. Use disease-free seed, rotate with non-host crops, and treat the seed with a recommended fungicide such as carboxin with thiram.

Loose smut

Loose smut, caused by Ustilago tritici, lives inside the seed and shows up at heading, when the ears are replaced by black spores. Because it is internally seed-borne, seed treatment works well: carboxin (Vitavax) at 2.5 g per kg of seed. Solar heat treatment is a non-chemical option: soak the seed for about four hours in the morning, then dry it in hot afternoon sun.

Spot blotch and wheat blast

Spot blotch, caused by Bipolaris sorokiniana, produces brown blotches that join up and cover the leaf. Crop rotation with non-host crops, healthy seed and seed treatment help, and partially resistant varieties should be used where available. Wheat blast is a newer threat: it was first detected in Bangladesh in February 2016, and in 2017 West Bengal banned wheat within five kilometres of the Bangladesh border in Murshidabad and Nadia districts to keep it out.

Major Diseases of Rice

Disease	Cause	Key symptoms	Main management
Blast	Magnaporthe oryzae (fungus)	Spindle-shaped leaf spots; nodes and panicle neck can rot	Resistant varieties; split nitrogen; field sanitation; fungicide spray
Bacterial leaf blight	Xanthomonas oryzae pv. oryzae (bacterium)	Leaf margins dry from the tip; bacterial ooze in the morning	Resistant varieties; split nitrogen; good drainage
Sheath blight	Rhizoctonia solani (fungus)	Blotches on the leaf sheath near the water line	Moderately resistant varieties; split nitrogen; fungicide spray
Brown spot	Bipolaris oryzae (fungus)	Brown spots on leaves and grains	Seed treatment; balanced nutrition; resistant varieties
False smut	Ustilaginoidea virens (fungus)	Grains become orange, then olive-green spore balls	Certified seed; moderate nitrogen; seed treatment
Bakanae	Fusarium fujikuroi (fungus)	Tall, thin seedlings that later rot	Seed treatment
Tungro	Two viruses, spread by the green leafhopper	Stunting; yellow to orange-yellow leaves	Resistant varieties; leafhopper control

Blast

Blast, caused by the fungus Magnaporthe oryzae, can attack the leaves (leaf blast), the nodes (node blast) and the neck of the panicle (neck blast), where it causes the most loss. The fungus survives on grassy weeds and on infected seedlings in nurseries. Avoid excess nitrogen and apply it in splits, keep fields and bunds free of weeds, and grow varieties recommended for your region. Fungicides are sprayed when the disease is seen in the field.

Bacterial leaf blight

Bacterial leaf blight, caused by Xanthomonas oryzae pv. oryzae, dries the leaf from the margins and tip. Drops of bacterial ooze are visible on the leaves early in the morning. The bacterium survives in seed, weeds, volunteer rice and stubble. Resistant varieties, split nitrogen, shallow water in the nursery, good drainage and clean fields are the main controls.

Sheath blight

Sheath blight, caused by Rhizoctonia solani, forms blotches on the leaf sheath. The fungus survives as hard resting bodies (sclerotia) in the soil and on crop debris. There are no highly resistant varieties, but moderately resistant ones help. Split nitrogen, skip the last nitrogen dose in infested fields, and use recommended fungicides such as hexaconazole or propiconazole when needed.

Brown spot

Brown spot, caused by Bipolaris oryzae, causes spots on leaves and grains and is linked to the Bengal famine of 1943. It is common in poorly fed crops and survives in soil and seed. Treat seed with captan or thiram at 4 g per kg, or with hot water at 55°C for 10 minutes; destroy stubble and weed hosts; and apply calcium silicate in silica-deficient soils.

False smut

False smut, caused by Ustilaginoidea virens, turns individual grains into spore balls that are orange at first and olive-green later. Use certified seed, avoid high nitrogen, and remove infected panicles and debris after harvest. Seed can be treated with carbendazim at 2 g per kg or with hot water at 52°C for 10 minutes.

Bakanae

Bakanae, caused by Fusarium fujikuroi, makes plants grow abnormally tall and thin before they rot. Reported losses range widely, and the disease is especially severe on Pusa Basmati 1121 and Pusa Basmati 1509 in Punjab and Haryana. Because it is seed-borne and soil-borne, treating the seed with a fungicide is the most important control.

Tungro

Tungro is caused by two viruses, rice tungro bacilliform virus and rice tungro spherical virus, and the green leafhopper (Nephotettix virescens) is the most efficient vector. Infected plants are stunted, tiller poorly and have yellow to orange-yellow leaves starting from the tip. Resistant varieties are the cheapest control. Light traps help monitor and reduce leafhoppers, and a fallow gap, adjusted planting dates and destruction of stubble break the cycle.

Major Diseases of Potato

Disease	Cause	Key symptoms	Main management
Late blight	Phytophthora infestans	Dark, water-soaked patches on leaves; brown rot in tubers	Protective spray before symptoms; systemic combination after; healthy seed; high ridges
Early blight	Alternaria solani	Dark spots with concentric rings on older leaves	Crop rotation; remove debris; fungicide spray
Black scurf	Rhizoctonia solani	Hard black crusts on tuber skin	Healthy seed; tuber treatment
Common scab	Streptomyces scabies (bacterium)	Rough, corky scab lesions on tubers	Disease-free seed; rotation; keep soil moist during tuber formation
Bacterial wilt (brown rot)	Ralstonia solanacearum (bacterium)	Plants wilt; tubers show brown rot	Clean seed; non-infested fields; rotation; good drainage
Viral diseases	PVY, PLRV and other viruses, spread by aphids	Mosaic, leaf rolling, stunting; yields fall each season	Virus-free seed; seed plot technique; aphid control; roguing

Late blight

Late blight, caused by Phytophthora infestans, is the most feared potato disease. It caused the Irish potato famine of the 1840s, and it thrives in cool, moist weather. Leaves develop dark patches that turn brown, and tubers rot.

• Plant healthy seed, grow the crop on high ridges, and keep fields well drained and free of weeds.
• Before any symptoms appear, spray a protective fungicide such as mancozeb when the weather turns favourable.
• Once symptoms appear, ICAR-CPRI advisories recommend combination products such as cymoxanil with mancozeb or dimethomorph with mancozeb, repeated about every 10 days depending on severity.
• Do not keep spraying the same fungicide; rotating products helps prevent resistance.
• Let the foliage dry fully before harvest and avoid contact between diseased foliage and tubers.

Early blight

Early blight, caused by Alternaria solani, forms dark spots with target-like concentric rings, usually on older leaves first. Rotate crops, remove and destroy infected debris, keep the crop well fed, and spray fungicides such as mancozeb or chlorothalonil when the disease appears.

Black scurf and common scab

Black scurf, caused by Rhizoctonia solani, leaves hard black crusts on the tuber skin and spreads through seed and soil; healthy seed and tuber treatment, for example with boric acid or pencycuron, are used against it. Common scab, caused by Streptomyces scabies, produces corky lesions and is worst in dry, alkaline soils. Use disease-free seed, rotate crops, and keep the soil moist during early tuber formation.

Bacterial wilt (brown rot)

Bacterial wilt, caused by Ralstonia solanacearum, makes plants wilt and tubers rot. It survives in soil, seed tubers and weeds, and there are no resistant varieties. Plant clean seed in fields with no history of the disease, rotate with non-host crops, control weeds and root-knot nematodes, and ensure good drainage.

Potato viruses and the seed plot technique

Viruses such as potato virus Y (PVY) and potato leafroll virus (PLRV) are spread by aphids, mainly Myzus persicae, and build up in seed tubers each season, so yields keep falling. Fourteen aphid species have been recorded on potato in India.

The seed plot technique, developed by ICAR-CPRI, Shimla, solves this for the plains. Seed potatoes are grown during the low-aphid period, from October to the first week of January, with healthy seed, insecticide sprays and roguing of diseased plants. The haulms are then cut, between late December and the second week of January, before aphid numbers rise.

Using Fungicides Safely

The chemical names in this guide are for awareness. Approvals and doses change, so always check before you buy or spray.

• Use only products registered for that crop and disease by the Central Insecticides Board and Registration Committee (CIB&RC), and follow the dose on the label.
• Ask your local Krishi Vigyan Kendra (KVK), state agricultural university or the Kisan Call Centre (1800-180-1551) for advice suited to your area.
• Wear gloves, a mask and full-sleeved clothing, and do not spray in strong wind.
• Rotate fungicides with different modes of action, and observe the waiting period before harvest.

Studying Plant Pathology

Plant disease management is taught in the B.Sc. (Hons.) Agriculture programme at SGT University, a four-year degree accredited by ICAR, where students diagnose diseases on a research farm of more than 55 acres and work in the faculty's entomology and genetics and plant breeding labs. Students who want to specialise can continue with:

• M.Sc. in Plant Pathology, for the diagnosis and management of crop diseases
• M.Sc. in Agricultural Entomology, for insect pests and the vectors that spread viruses such as tungro and potato viruses
• M.Sc. in Genetics and Plant Breeding, for developing disease-resistant varieties

Related reading: types of soil in India, types of farming in India and government jobs after B.Sc Agriculture. You can also learn more about the Faculty of Agricultural Sciences.

Key Takeaways

• Wheat's main diseases are the three rusts, Karnal bunt, loose smut and spot blotch; yellow rust is the biggest threat in cool, damp weather in north-west India.
• Rice's main diseases are blast, bacterial leaf blight, sheath blight, brown spot, false smut, bakanae and tungro.
• Potato's main diseases are late blight, early blight, black scurf, common scab, bacterial wilt and viruses.
• Resistant varieties and healthy seed are the first line of defence for all three crops.
• Seed treatment controls seed-borne diseases such as loose smut, bakanae and brown spot.
• Use only registered fungicides at the label dose, and seek local advice from a KVK or agricultural university.

FAQs

Q1. What are the major diseases of wheat in India?
The major wheat diseases in India are the three rusts (yellow or stripe rust, brown or leaf rust, and black or stem rust), Karnal bunt, loose smut, spot blotch and powdery mildew. Wheat blast is a newer threat, first seen in neighbouring Bangladesh in 2016.

Q2. What are the major diseases of rice?
The major rice diseases are blast, bacterial leaf blight, sheath blight, brown spot, false smut, bakanae and tungro. Blast, caused by the fungus Magnaporthe oryzae, can attack the leaves, the nodes and the neck of the panicle.

Q3. What causes late blight of potato?
Late blight is caused by Phytophthora infestans, which thrives in cool, moist weather. The same disease caused the Irish potato famine of the 1840s. It turns leaves brown, rots tubers and spreads fast in favourable weather.

Q4. How do you control yellow rust in wheat?
Grow resistant varieties, destroy volunteer wheat plants, and inspect the crop during cool, damp weather. When yellow rust appears in patches, ICAR-IIWBR advises spraying a fungicide; propiconazole and tebuconazole are among those used. Follow the label dose.

Q5. How is loose smut of wheat controlled?
Loose smut is carried inside the seed, so it is controlled through the seed. Use disease-free seed and treat it with carboxin (Vitavax) at 2.5 g per kg of seed. Solar heat treatment of seed is a non-chemical option.

Q6. What is Karnal bunt?
Karnal bunt is a wheat disease caused by the fungus Tilletia indica. Infected grains are partly turned into a black, powdery mass. It lowers grain quality and is a quarantine concern in the international wheat trade.

Q7. What is bakanae disease of rice?
Bakanae is caused by Fusarium fujikuroi. Infected plants grow abnormally tall and thin and later rot. It is especially severe on Pusa Basmati 1121 and Pusa Basmati 1509 in Punjab and Haryana. It is seed-borne and soil-borne, so seed treatment is the main control.

Q8. What is rice tungro and how does it spread?
Tungro is a disease caused by two viruses, rice tungro bacilliform virus and rice tungro spherical virus. The green leafhopper spreads it. Infected plants are stunted, with yellow to orange-yellow leaves. Resistant varieties and leafhopper control are the main defences.

Q9. What is the seed plot technique in potato?
The seed plot technique, developed by ICAR-CPRI, Shimla, grows seed potatoes in the plains during the period when aphids are scarce, from October to the first week of January. Combined with roguing and cutting the haulms on time, it keeps seed potatoes free of aphid-borne viruses.

Q10. When are wheat, rice and potato diseases most likely?
Rice diseases build up in the warm, humid kharif season. Wheat diseases appear in the rabi season, with yellow rust most likely in cool, damp weather from winter into early spring. Potato late blight strikes during cool, moist spells in winter.